1. Field of the Invention
The present invention relates to a process for producing a monoalkenylbenzene. More particularly, it pertains to a process for producing a monoalkenylbenzene by subjecting an aromatic hydrocarbon compound having at least one hydrogen atom bonded at a-position of the side chain to side-chain alkenylation by the use of a conjugated diene having 4 or 5 carbon atoms. A monoalkenylbenzene is useful as the starting intermediate material for various organic compounds typified by high molecular monomers and pharmaceutical preparations. As an example, 5-(o-tolyl)-2-pentene that is produced from o-xylene and 1,3-butadiene can be converted into industrially useful 2,6-naphthalene-dicarboxylic acid by ring closure followed by dehydrogenation, isomerization and oxidation.
2. Description of Related Arts
As a process for producing a monoalkenylbenzene by subjecting an aromatic hydrocarbon compound to side-chain alkenylation by the use of a conjugated diene having 4 or 5 carbon atoms, there is known the process in which is employed as a catalyst an alkali metal such as sodium and potassium or an alloy thereof.
For example, German Patent No. 557514 discloses the use of metallic sodium as a catalyst in the above-mentioned process and Eberhardt et al. describes the use of metallic sodium supported on an alkaline earth metal oxide as a catalyst in J. Org. Chem., vol. 30 (1965), pp 82 to 84.
Likewise, there are disclosed the use of metallic potassium in Japanese Patent Publication No. 17973/1975, the use of a potassium/sodium alloy or a mixture of metallic potassium and metallic sodium in Japanese Patent Publication Nos. 17975/1975 and 8930/1976, and the use of metallic potassium supported on an alkali metal oxide or an alkaline earth metal oxide in U.S. Pat. No. 3,244,758 and the aforementioned J. Org. Chem., vol. 30 (1965), pp 82 to 84, each as the catalyst in the above-mentioned process.
There is also disclosed the use of the mixture obtained by heat treating a potassium compound and metallic sodium at 300.degree. C. or a temperature not lower than 350.degree. C. as the catalyst in the above-mentioned process in Japanese Patent Application Laid-Open Nos. 27929/1972 and 31935/1972.
Among the aforestated processes, the process in which is used as a catalyst metallic sodium with or without being supported on an alkaline earth metal oxide is impractical because of insufficiency in both catalytic activity and selectivity of reaction. The process in which is used as a catalyst, metallic potassium, a potassium/sodium alloy or a mixture of metallic potassium and metallic sodium exhibits a high catalytic activity but causes violent reaction of the catalyst with oxygen, moisture and the like. Therefore, an attempt to put the aforesaid process into industrial practice involves various problems on safety due to possible hazards such as fire and explosion.
Likewise, the process in which metallic potassium which is supported on the oxide of an alkali metal or an alkaline earth metal is used as a catalyst involves various problems on safety due to the use of the extremely combustible metallic potassium when put into industrial practice.
On the other hand, the process in which is used as a catalyst the mixture obtained by heat treating a potassium compound and metallic sodium at a high temperature is characterized in that metallic potassium or a potassium alloy is not employed, but can not be said to be necessarily practical because of insufficient catalytic activity and the necessity for treating the highly inflammable substance at a high temperature.